1. Field of the Invention
This invention relates to an optical recording medium, particularly to an optical recording medium for recording layer comprising at least one asymmetric trimethine-cyanine dye with specific functional group and an additive, which can enhance the writing sensitivity of DVD-R.
2. Description of the Related Art
An optical recording medium capable of once recording by a laser ray has been known. In the structure of the CD-R recording medium, a recording layer comprising an organic dye, a reflection layer and a protective layer are laminated on a transparent substrate by order. The recording information on the disc is performed by irradiating a laser at a wavelength of 780 nm to 830 nm to cause exothermic deformation of the recording layer. The information is usually reproduced by irradiating with the same laser ray, and the reflecting difference between the recorded area and unrecorded area is detected for the recording layer.
It is known that a laser ray with a shorter wavelength has a reduced light spot. Therefore, studies have being made to develop the optical disc capable of recording and reproducing by a laser beam of a wavelength of 620 nm to 690 nm to increase the recording density. Recordable digital video (DVD-R), which is capable of recording and reading in high density, is propagated as new media of the next generation. Since the wavelength zone for performing the recording and reproducing in DVD-R differs from that of the CD-R, the criteria for selecting the recording material to be employed for the CD-R cannot be applied to the DVD-R. Hence, new selection criteria are required to be established from a viewpoint peculiar to the DVD-R.
Trimethine-based cyanine dye is a popular material for the DVD-R recording layer. U.S. Pat. No. 5,976,658, and U.S. Pat. No. 6,291,045 described the use of trimethine-based cyanine dye having symmetry or asymmetry indolenine structure for DVD-R. However, the dye material should be selected carefully, while the writing wavelength of laser beam of DVD-R machines is changed from 635 nm to 650 nm (or further). Because the wavelength of laser power is getting longer, the dye absorbance of film state for 650 nm should be increased a little more. The dye, which is suitable for writing wavelength of 635 nm laser beam, is not performed well while the writing wavelength of laser beam is 650 nm because of low sensitivity at the region that might cost higher writing power to record information or record failed.
Said in U.S. Pat. No. 6,338,888, increase the sensitivity of recording could be reached by increasing the absorption of organic layer at the wavelength of writing laser. According to the opinion, we declare a new composition with specific additives which could enhance the recording sensitivity.
The first object of the present invention is to provide an asymmetric indolenine cyanine dye with electron-withdrawing group which is substituted on one ring of indolenine or benzoindolenine by the formula [1], [2], [3], [4], which are shown in scheme 1. 
The second object of the present invention is to provide an optical recording medium with a recording layer, which comprises at least one asymmetric trimethine-cyanine dye with electron-withdrawing substituted group (EWG) and an additive which is a kind of asymmetric trimethine-cyanine dye with electron-donating substituted group (EDG).
The third object of the present invention is to provide a process to prepare asymmetric trimethine-cyanine dye with electron-withdrawing group and the one with electron-donating substituted group (EDG).
The fourth object of the present invention is to provide an optical recording medium with improved write/read characteristics at the writing wavelength of 650 nm or further.
According to the invention, the asymmetric trimethine-cyanine dye with electron-withdrawing substituted group used in the recording layer is any one represented by the general formulas [1], [2], [3], and [4] which were shown in scheme 1. xe2x80x9cEWGxe2x80x9d represents any electron-withdrawing substituted group, such as cyano and nitro group. xe2x80x9cR3xe2x80x9d and xe2x80x9cR2xe2x80x9d are independently selected from substituted or unsubstitued alkyl, phenyl, benzyl, alkylphenyl and phenoxyalkyl group. xe2x80x9cR3xe2x80x9d and xe2x80x9cR4xe2x80x9d are independently selected from hydrogen atom, halogen atom, alkoxy, hydroxyl or alkyl group. xe2x80x9cYxe2x80x9d is selected from hydrogen atom, halogen atom or alkyl group, and xe2x80x9cXxe2x80x9d is an anion selected from the group consisting of Fxe2x88x92, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, ClO4xe2x88x92, BF4xe2x88x92, PF6xe2x88x92, SbF6xe2x88x92, OTsxe2x88x92, OMsxe2x88x92, SCNxe2x88x92, alkylsulfonate and alkylcarboxylate. The material has a maximum absorption wavelength from 575 nm to 600 nm. It is used as a recording material for DVD-R machine with the laser wavelength from 620 nm to 690 nm.
The material used in the recording layer also selectively comprises the trimethine-cyanine dye of the following general formula [5]: 
xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d, may be the same or different from each other, represent any one of the following general formulas [6], [7], [8], and [9]: 
xe2x80x9cDxe2x80x9d may be any one of the substituted or unsubstitued alkyl, carboxyl, alkoxycarbonyl, alkylcarboxyl, alkoxyl, alklhydroxyl, aralkyl, alkenyl, alkylamide, alkylamino, alkylsufonamide, alkylcarbamoyl, alkylsulfamoyl, hydroxyl, halogen atom, hydrogen atom, alkylalkoxyl, alkylhalide, alkylsulfonyl, alkylcarboxyl or alkylsulfonyl which are bonded to a metallic ion or alkyl, phenyl, benzyl, alkylphenyl or phenoxyalkyl group. xe2x80x9cpxe2x80x9d represents the number of substituent groups, which is an integer of 1 or more.
xe2x80x9cR5xe2x80x9d and xe2x80x9cR6xe2x80x9d may be the same or different from each other and are individually substituted or unsubstitued alkyl, phenyl, benzyl, alkylphenyl or phenoxyalkyl group. xe2x80x9cZxe2x80x9d is hydrogen atom, halogen atom or alkyl group, and xe2x80x9cXxe2x80x9d is an anion selected from the group consisting of Fxe2x88x92, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, ClO4xe2x88x92, BF4xe2x88x92, PF6xe2x88x92, SbF6xe2x88x92, OTsxe2x88x92, OMsxe2x88x92, SCNxe2x88x92, alkylsulfonate, and akylcarboxylate.
The material as an additive used in the dye layer also selectively comprises any trimethine-cyanine dye represented by the following general formulas [10], [11], [12], and [13]: 
xe2x80x9cEDGxe2x80x9d represents any electron-donating substituted group such as amino, alkylamino, and methoxy group. xe2x80x9cR7xe2x80x9d and xe2x80x9cR8xe2x80x9d are the same or different from each other and are individually substituted or unsubstitued alkyl, phenyl, benzyl, alkylphenyl and phenoxyalkyl group. xe2x80x9cR9xe2x80x9d and xe2x80x9cR10xe2x80x9d are independently selected from hydrogen atom, halogen atom, cyano or nitro group. xe2x80x9cYxe2x80x9d is hydrogen atom, halogen atom or alkyl group, and xe2x80x9cXxe2x80x9d is an anion selected from the group consisting of Fxe2x88x92, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, ClO4xe2x88x92, BF4xe2x88x92, PF6xe2x88x92, SbF6xe2x88x92, OTsxe2x88x92, OMsxe2x88x92, SCNxe2x88x92, alkylsulfonate and alkylcarboxylate. The material has a maximum absorption wavelength from 575 nm to 620 nm. It is used as a recording material for DVD-R machine with the laser wavelength from 620 nm to 690 nm. The dye layer comprising not only the trimethine-cyanine dye containing xe2x80x9cEWGxe2x80x9d but also the trimethine-cyanine dye containing xe2x80x9cEDGxe2x80x9d has the advantage of increasing the recording sensitivity, so that the writing power of laser can be reduced while recording information in DVD-R.
The method of preparing dye solution according to this invention can be described as follows.
(1) A cyanine dye represented by general formula [1], [2], [3], or [4] was dissolved in an organic solvent, such as fluorinated alcohol, diaceton alcohol, methylethyl ketone, methanol, toluene, cyclohexanone, acetylacetone, and dioxane. The concentration of the dye solution was 0.5% to 20% by weight.
(2) A dye mixture, which contains cyanine dye represented by general formula [1], [2], [3], or [4] mixed with the dye of formula [5] that is less than 100% by weight, was dissolved in an organic solvent such as fluorinated alcohol, diaceton alcohol, methylethyl ketone, methanol, toluene, cyclohexanone, acetylacetone, and dioxane. The concentration of the dye solution was 0.5% to 20% by weight.
(3) A dye mixture, which contains cyanine dye represented by general formula [1], [2], [3], or [4] mixed with the dye of formula [10], [11], [12] or [13] that is less than 50% by weight, was dissolved in an organic solvent such as fluorinated alcohol, diaceton alcohol, methylethyl ketone, methanol, toluene, cyclohexanone, acetylacetone, and dioxane. The concentration of the dye solution was 0.5% to 20% by weight.
(4) A dye mixture, which contains cyanine dye represented by general formula [5] mixed with the dye of formula [10], [11], [12] or [13] that is less than 50% by weight, was dissolved in an organic solvent, such as fluorinated alcohol, diaceton alcohol, methylethyl ketone, methanol, toluene, cyclohexanone, acetylacetone, and dioxane. The concentration of the dye solution was 0.5% to 20% by weight.
(5) A dye mixture, which contains cyanine dye represented by [1], [2], [3], [4] mixed with the dye of formula [5] that is less than 100% and the dye of formula [10], [11], [12] or [13] that is less than 50% by weight, was dissolved in an organic solvent such as fluorinated alcohol, diaceton alcohol, methylethyl ketone, methanol, toluene, cyclohexanone, acetylacetone, and dioxane. The concentration of the dye solution was 0.5% to 20% by weight.
The manufacture of the optical recording medium according to this invention can be performed as follows.
(1) The material for the substrate may be employed by glass, epoxy resin, methacrylate resin, polycarbonate, polyester resin, polyvinyl chloride resin, polyolefin resin. The substrate may be provided with tracking grooves or pits.
(2) The dye solution is provided on a substrate by means of a spin-coating method.
(3) The optical recording medium may further include a reflection layer in addition to the recording layer. The reflection layer, a film of high reflectivity, can be formed by the vapor-deposition or sputtering a metal, such as Gold, Aluminum, Silver, Cupper, Platinum, alloy or multi-reflective layer.
(4) The reflection layer may be provided with protective layer. It is formed for the purpose of protecting or improving the optical recording medium, and can be formed by coating a solution of a radiation cure type resin on a given surface and then by radiation-curing the coater layer.
(5) The optical recording medium may be a single-sided recording medium obtained by laminating a single-side substrate and a non-grooved substrate with an adhesion. The single-sided optical recording medium being prepared by process (1) to (5).
(6) The optical recording medium may be a double-sided recording medium obtained by laminating two single-sided optical recording medium with an adhesion. The single-sided optical recording medium being prepared by process (1) to (5).
Other objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred but non-limiting embodiment. The following description is made with reference to the accompanying drawings.
The invention will be further explained in detail with reference to the following preferred embodiments.
Asymmetric dyes, which are trimethine-cyanine dyes substituted with different structure comprising electron-withdrawing group (EWG), could be synthesized by different methods suggested in J. Org. Chem. 1995, 60, 2411 and U.S. Pat. No. 6,306,478. For example, xe2x80x9cEWGxe2x80x9d is a nitro group, while xe2x80x9cR3xe2x80x9d and xe2x80x9cYxe2x80x9d are hydrogen groups in the formula [1]. A modified method is designed as shown in scheme 2, wherein the reactive condition is under atmosphere and yield of formula [1] is high. 
In the reaction of scheme 2, high yield of formula [15] and formula [16] could be easily achieved by using well-known alkylation and nitration processes, respectively. Then, formula [16] is dissolved in alcohol solvent and is mixed with N,N-diphenylformamidine under refluxing. Next, formula [17] is obtained with ideal quality and yield. Finally, formula [17] and formula [18] are treated with the basic solvent and stirred at room temperature; consequently, formula [1] is obtained in high yield.
Examples of the compounds of the formulas of [1], [2], [3], and [4], which are synthesized by the similar method in scheme 2, are listed in Tables 1.
The material used in the dye layer also selectively comprises the trimethine-cyanine dye of the following general formula [5]: 
xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d represent any one of the following formulas [6], [7], [8], and [9]: 
xe2x80x9cAxe2x80x9d and xe2x80x9cBxe2x80x9d may be the same or different from each other. xe2x80x9cDxe2x80x9d may be any one of the substituted or unsubstitued alkyl, carboxyl, alkoxycarbonyl, alkylcarboxyl, alkoxyl, alklhydroxyl, aralkyl, alkenyl, alkylamide, alkylamino, alkylsufonamide, alkylcarbamoyl, alkylsulfamoyl, hydroxyl, halogen atom, hydrogen atom, alkylalkoxyl, alkylhalide, alkylsulfonyl, alkylcarboxyl or alkylsulfonyl which are bonded to a metallic ion or alkyl, phenyl, benzyl, alkylphenyl or phenoxyalkyl group. xe2x80x9cpxe2x80x9d represents the number of substituent groups, which is an integral of 1 or more.
xe2x80x9cR5xe2x80x9d and xe2x80x9cR6xe2x80x9d may be the same or different from each other and are individually the substituted or unsubstitued alkyl, phenyl, benzyl, alkylphenyl or phenoxyalkyl group. xe2x80x9cZxe2x80x9d is hydrogen atom, halogen atom or alkyl group, and xe2x80x9cXxe2x88x92xe2x80x9d is an anion selected from the group consisting of Fxe2x88x92, Clxe2x88x92, Brxe2x88x92, Ixe2x88x92, ClO4xe2x88x92, BF4xe2x88x92, PF6xe2x88x92, SbF6xe2x88x92, OTsxe2x88x92, OMsxe2x88x92, SCNxe2x88x92, alkylsulfonate, and akylcarboxylate.
The material used in the dye layer could also comprise at least one trimethine-cyanine dye with electron-donating substituted group (EDG), and depicted in the following general formulas [10], [11], [12], and [13]. The dye layer comprising not only the trimethine-cyanine dye containing xe2x80x9cEWGxe2x80x9d but also the trimethine-cyanine dye containing xe2x80x9cEDGxe2x80x9d has the advantage of increasing the recording sensitivity, so that the writing power of laser can be reduced while recording information in DVD-R. 
For example, xe2x80x9cEDGxe2x80x9d is an amino group, while xe2x80x9cR3xe2x80x9d and xe2x80x9cYxe2x80x9d of the formula [1] are hydrogen groups, as shown in the formula [10]. By the reduction of the nitro constituent in the formula [1] with reductant, such as SnCl2, H2O, Fe/HCl, formula [10] was obtained, as depicted in Scheme 3. It is noted that xe2x80x9cR1xe2x80x9d and xe2x80x9cR2xe2x80x9d of formula [10] in Scheme 3 are in the same position as xe2x80x9cR7xe2x80x9d and xe2x80x9cR8xe2x80x9d. 
Examples of the compounds of the formula [10], which are synthesized by the similar method in table 2, are given below.
In another example, xe2x80x9cEDGxe2x80x9d is a substituted alkylamino group, while xe2x80x9cR3xe2x80x9d and xe2x80x9cYxe2x80x9d (of formula [1]) are hydrogen groups in the formula [10]. By alkylating the amino constituent in the formula [10] with alkyl halide, an alkylamino substituted compound in formula [10] was obtained, as shown in Scheme 4. 
Examples of the compounds of the formula of [10xe2x80x2], which are synthesized by the similar method in scheme 4, are given in Table 3.
A polycarbonate substrate is provided with a track pitch 0.74 xcexcm and only wobble signal (pre-pit may also be included) is employed.
The dye solution can be prepared according to one of the following method:
(1) a cyanine dye represented by general formula [1], [2], [3], or [4] was dissolved in an organic solvent;
(2) a dye mixture, which contains cyanine dye represented by general formula [1], [2], [3], or [4] mixed with the dye of formula [5] that is less than 100% by weight, was dissolved in an organic solvent;
(3) a dye mixture, which contains cyanine dye represented by general formula [1], [2], [3], or [4] mixed with the dye of formula [10], [11], [12] or [13] that is less than 50% by weight, was dissolved in an organic solvent;
(4) a dye mixture, which contains cyanine dye-represented by general formula [5] mixed with the dye of formula [10], [11], [12] or [13] that is less than 50% by weight, was dissolved in an organic solvent; and
(5) a dye mixture, which contains cyanine dye represented by [1], [2], [3], [4] mixed with the dye of formula [5] that is less than 100% and the dye of formula [10], [11], [12] or [13] that is less than 50% by weight, was dissolved in an organic solvent.
The organic solvent is selected from the group consisting of fluorinated alcohol, diaceton alcohol, methylethyl ketone, methanol, toluene, cyclohexanone, acetylacetone and dioxane. Also, the concentration of the dye solution was in the range from about 0.5% to 20% by weight.
The dye solution according to the above description might further comprise some kinds of singlet oxygen quencher, such as a metal complex, a light absorbent, a radical scavenger, etc. Then, the substrate is spin-coated with the dye solution at a rotational frequency of 3000 rpm, and then is dried at 70xc2x0 for 20 minutes to form a recording layer consisting of a photosensitive dye film with a thickness of 100 nm, approximately.
The material for the substrate may be employed by glass, epoxy resin, methacrylate resin, polycarbonate, polyester resin, polyvinyl chloride resin, or polyolefin resin. Also, the substrate may be provided with tracking grooves or pits.
Thereafter, a reflection layer is deposited on the recording layer by sputtering. The reflection layer, a metal film with high reflectivity such as Gold, Aluminum, Silver, Cupper, Platinum, and alloy, can be formed by the vapor-deposition or sputtering. Also, the reflection layer could be the multi-reflective layer.
A protective layer comprising an ultraviolet-curing resin is further spin-coated on the reflection layer. The protective layer is formed for the purpose of protecting or improving the optical recording medium, and can be formed by coating a solution of a radiation cure type resin on a given surface and then by radiation-curing the coater layer.
Then a pair of the optical discs thus obtained is superimposed via an adhesive layer comprising an ultraviolet-curing resin, and thereby a laminated-disc is obtained.
It is noted that the optical recording medium could be a single-sided recording medium obtained by laminating a single-side substrate and a non-grooved substrate with an adhesion, or could be a double-sided recording medium obtained by laminating two single-sided optical recording medium with an adhesion.
Next, a laser beam of 650 nm or further is irradiated to the optical discs to form the recording signals with improved characteristics, such as modulation amplitude, jitter and wide power margin.
This invention will be further explained in detail with reference to the following examples.
First, to synthesize
N-propyl-2-(2-anilidovinyl)-3,3-dimethyl-5-nitroindol inium chlorate [17-1], 
1-propyl-2,3,3-trimethyl-5-nitroindoleninum chlorate (23 g), N,N-diphenylformamidine (20g) and 1-octanol (70 mL) are mixed in a 500 mL round bottle with a condenser. The mixture is refluxed for 24 hr. The formula [17-1] (15 g) is obtained as a brown color crystal while the room temperature is reached. The 1H NMR spectrum is measured by the machine of 300 MHz. The result is: xcex4 1.04 (t, J=7.4 Hz, 3H), 1.85 (s, 6H), 4.15 (t, J=7.4 Hz, 2H), 6.30 (d, J=12.1 Hz, 1H), 7.40 (t, J=7.2 Hz, 1H), 7.53-766 (m, 4H), 7.79 (d, J=8.85 Hz, 1H), 8.40 (dd, J=12.1, 2.3 Hz, 1H), 8.68 (d, J=2.3 Hz, 1H) and 8.88 (d, J=12.1 Hz, 1H).
Second, the compound of formula [17-1] (12 g), 1-butyl-2,3,3-trimethylbenzo(e) indoleninium chlorate (9 g) and Pyridine (20 mL) are mixed by stirring at room temperature for 3 hr. Then, the solution is poured into 10% H2SO4 solution. The formula [1-19] (15 g) is obtained by filtering and crystallizing with MeOH. The spectrum result is xcexmax (TFP)=577 nm; 1H NMR (300 MHz, CDCl3) xcex4 0.99 (t, J=7.2 Hz, 3H), 1.06 (t, J=7.2 Hz, 3H), 1.53-1.61 (m, 4H), 1.78 (s, 6H), 1.92 (quin., J=7.2 Hz, 3H), 2.03 (s, 6H), 4.10 (t, J=7.2 Hz, 3H), 4.42 (t, J=7.2 Hz, 3H), 6.89 (d, J=13.5 Hz, 1H), 7.07 (d, J=8.8 Hz, 1H), 7.13 (d, J=13.5 Hz, 1H), 7.47 (d, J=8.8 Hz, 1H), 7.54 (t, J=7.6 Hz, 1H), 7.66 (t, J=7.6 Hz, 1H), 7.97-8.02 (m, 1H), 8.13 (d, J=8.6 Hz, 1H), 8.16 (d, J=2.1 Hz, 1H), 8.29 (dd, J=8.6, 2.1 Hz, 1 H), 8.51 (t, J=13.5 Hz, 1H).
Third, the compound of formula [1-19] (5.7 g), Tin chloride dihydrate (10.5 g) were dissolved in EtOH (40 mL), then the mixture was heated under refluxing for 6 hr. After cooling down to room temperature, the solution was poured into 10% NaOH solution. The formula [10-3] (4.5 g) is obtained by filtering and crystallizing with MeOH. The spectrum result is xcexmax (TFP)=576 nm; 1H NMR (300 MHz, CDCl3) xcex4 0.95-1.02 (m, 6H), 1.46-1.58 (m, 4H), 1.73 (s, 6H), 1.76-1.90 (m, 4H), 2.01 (s, 6H), 4.07 (t, J=7.4 Hz, 2H), 4.15 (t, J=7.4 Hz, 2H), 6.38-6.47 (m, 2H), 6.69 (dd, J=2.2, 8.4 Hz, 1H), 6.90-6.93 (m, 2H), 7.28-7.34 (m, 1H), 7.40-7.47 (m, 1H), 7.6 (t, J=11 Hz, 1H), 7.94 (d, J=8.9 Hz, 2H), 8.10 (d, J=8.9 Hz, 1H), 8.42 (t, J=13.5 Hz, 1H).
Fourth, the compound of formula [10-3] (5.7 g), n-Propyl Iodide (3.3 g) were dissolved in Ethyl Acetate (20 mL), then the mixture was heated under reflux for 24 hr. After cooling down to room temperature, the solution was poured into 10% NaOH solution. The formula [10xe2x80x2-3] (4.0 g) is obtained by filtering and crystallizing with MeOH. The spectrum result is xcexmax (TFP)=580 nm; 1H NMR (300 MHz, CDCl3) xcex4 0.98-1.13 (m, 12H), 1.50-1.63 (m, 2H), 1.74 (s, 6H), 1.84-1.96 (m, 4H), 2.0 (s, 6H), 3.03-3.16 (m, 2H), 3.88-4.21 (m, 4H), 6.57-6.76 (m, 4H), 6.98 (d, J=8.5 Hz, 1H), 7.33 (d, J=8.8 Hz, 1H), 7.44 (t, J=7.5 Hz, 1H), 7.59 (t, J=7.5 Hz, 1H), 7.92 (dd, J=4.0, 8.0 Hz, 2H), 8.10 (d, J=8.5Hz, 1H), 8.41 (t, J=13.5 Hz, 1H).
There are five experiments, Examples 1, 2, 3 and Comparative Examples 1, 2, conducted in Disc Test 1, and the results are summarized in Table 4. The experimental details are described as follows.